I would be careful, some small puppies can have seizures after using flea dips. I would just use dawn soap detergent, rub it on him for like five minutes then rinse, this works great....
Can I Give My 7 Week Old Puppy A Flea Dip?
Please let the vet do that,it all depends on the weight of the puppy. Dawn dish soap is the best!! It is safe and I promiss you will love it and so will the puppy just don't get in the eyes!!